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Huge Inverse Magnetization Generated by Faraday Induction in Nano-Sized Au@Ni Core@Shell Nanoparticles.

Kuo CC, Li CY, Lee CH, Li HC, Li WH - Int J Mol Sci (2015)

Bottom Line: The magnitude of the induced inverse magnetization is very sensitive to the field reduction rate as well as to the thermal and field processes before turning the magnetic field off, and can be as high as 54% of the magnetization prior to cutting off the applied magnetic field.Memory effect of the induced inverse magnetization is clearly revealed in the relaxation measurements.The key to these effects is to have the induced eddy current running beneath the amorphous Ni shells through Faraday induction.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, National Central University, Jhongli 32001, Taiwan. s751734@hotmail.com.

ABSTRACT
We report on the design and observation of huge inverse magnetizations pointing in the direction opposite to the applied magnetic field, induced in nano-sized amorphous Ni shells deposited on crystalline Au nanoparticles by turning the applied magnetic field off. The magnitude of the induced inverse magnetization is very sensitive to the field reduction rate as well as to the thermal and field processes before turning the magnetic field off, and can be as high as 54% of the magnetization prior to cutting off the applied magnetic field. Memory effect of the induced inverse magnetization is clearly revealed in the relaxation measurements. The relaxation of the inverse magnetization can be described by an exponential decay profile, with a critical exponent that can be effectively tuned by the wait time right after reaching the designated temperature and before the applied magnetic field is turned off. The key to these effects is to have the induced eddy current running beneath the amorphous Ni shells through Faraday induction.

No MeSH data available.


Related in: MedlinePlus

(a) Temperature dependencies of the magnetization collected at temperatures measured in steps of 2 K in the processes starting with cooling (open triangles) from 300 K with Ha = 200 Oe. The W’s at 200, 100, 40 and 20 K mark the process of turning the Ha off at a rate of RH = −50 Oe/s for 3 min, after waiting for 30 min upon reaching that temperature. The arrows indicate the directions of the temperature-changing processes. The open circles indicate the magnetization measured in warming, after waiting for 2 min upon reaching 2 K. (b) Low temperature portions of the M(T) curves displayed in (a), showing step-like increases of M around 15 and 35 K, where Ha has been turned off during cooling. No such behaviors are observed around 100 and 200 K.
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ijms-16-20139-f008: (a) Temperature dependencies of the magnetization collected at temperatures measured in steps of 2 K in the processes starting with cooling (open triangles) from 300 K with Ha = 200 Oe. The W’s at 200, 100, 40 and 20 K mark the process of turning the Ha off at a rate of RH = −50 Oe/s for 3 min, after waiting for 30 min upon reaching that temperature. The arrows indicate the directions of the temperature-changing processes. The open circles indicate the magnetization measured in warming, after waiting for 2 min upon reaching 2 K. (b) Low temperature portions of the M(T) curves displayed in (a), showing step-like increases of M around 15 and 35 K, where Ha has been turned off during cooling. No such behaviors are observed around 100 and 200 K.

Mentions: A memory effect in the magnetization was revealed below the blocking temperature but not above, as demonstrated in the relaxation measurements shown in Figure 8a,b. These M(T) loops were collected in the processes beginning with the slow cooling from 300 K in Ha = 200 Oe. Magnetization was recorded in steps of 2 K after the temperature was stabilized. Cooling was temporarily stopped for 30 min upon reaching 200 K, followed by turning the Ha off at a rate of –50 Oe/s to allow the magnetization to relax downward for 3 min. Cooling was resumed after reapplying Ha to reach 200 Oe. The same process of temporarily stopping the cooling and turning the Ha off-and-on was conducted at 100, 40 and 20 K. There was a 2 min wait upon reaching the base temperature of 2 K before warming the sample to 300 K using the same temperature steps. Interestingly, the M(T) curve taken in the warming process displays step-like increases at 15 K (by 6%) and 35 K (by 1%), where Ha was temporarily terminated in the cooling process (Figure 8b). No abrupt changes of M were observed at 100 and 200 K. Note that the time interval between the cooling and warming processes at 20, 40, 100 and 200 K are 82, 172, 355 and 617 min, respectively. It appears that the memory effect could last for 172 min, as it does appear around 40 K. The disappearance of the memory behavior at 100 and 200 K could be because the time interval has exceeded the time that the memory can last or that the temperatures are well above TB. The memory effect in nanoparticle systems has been attributed to the existence of significant dipole interactions among particle superspins and/or the broad distribution of relaxation times in the NP assembly [25]. In the present case, the NPs are very loosely packed and the interparticle interaction is insignificant. Size polydispersity of the assembly then plays a major role in the appearance of the memory effect. The anisotropy energy barriers for random flips of domain superspins can generate not only stretched exponential relaxation of the induced magnetization but also give rise to the memory effect.


Huge Inverse Magnetization Generated by Faraday Induction in Nano-Sized Au@Ni Core@Shell Nanoparticles.

Kuo CC, Li CY, Lee CH, Li HC, Li WH - Int J Mol Sci (2015)

(a) Temperature dependencies of the magnetization collected at temperatures measured in steps of 2 K in the processes starting with cooling (open triangles) from 300 K with Ha = 200 Oe. The W’s at 200, 100, 40 and 20 K mark the process of turning the Ha off at a rate of RH = −50 Oe/s for 3 min, after waiting for 30 min upon reaching that temperature. The arrows indicate the directions of the temperature-changing processes. The open circles indicate the magnetization measured in warming, after waiting for 2 min upon reaching 2 K. (b) Low temperature portions of the M(T) curves displayed in (a), showing step-like increases of M around 15 and 35 K, where Ha has been turned off during cooling. No such behaviors are observed around 100 and 200 K.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4613193&req=5

ijms-16-20139-f008: (a) Temperature dependencies of the magnetization collected at temperatures measured in steps of 2 K in the processes starting with cooling (open triangles) from 300 K with Ha = 200 Oe. The W’s at 200, 100, 40 and 20 K mark the process of turning the Ha off at a rate of RH = −50 Oe/s for 3 min, after waiting for 30 min upon reaching that temperature. The arrows indicate the directions of the temperature-changing processes. The open circles indicate the magnetization measured in warming, after waiting for 2 min upon reaching 2 K. (b) Low temperature portions of the M(T) curves displayed in (a), showing step-like increases of M around 15 and 35 K, where Ha has been turned off during cooling. No such behaviors are observed around 100 and 200 K.
Mentions: A memory effect in the magnetization was revealed below the blocking temperature but not above, as demonstrated in the relaxation measurements shown in Figure 8a,b. These M(T) loops were collected in the processes beginning with the slow cooling from 300 K in Ha = 200 Oe. Magnetization was recorded in steps of 2 K after the temperature was stabilized. Cooling was temporarily stopped for 30 min upon reaching 200 K, followed by turning the Ha off at a rate of –50 Oe/s to allow the magnetization to relax downward for 3 min. Cooling was resumed after reapplying Ha to reach 200 Oe. The same process of temporarily stopping the cooling and turning the Ha off-and-on was conducted at 100, 40 and 20 K. There was a 2 min wait upon reaching the base temperature of 2 K before warming the sample to 300 K using the same temperature steps. Interestingly, the M(T) curve taken in the warming process displays step-like increases at 15 K (by 6%) and 35 K (by 1%), where Ha was temporarily terminated in the cooling process (Figure 8b). No abrupt changes of M were observed at 100 and 200 K. Note that the time interval between the cooling and warming processes at 20, 40, 100 and 200 K are 82, 172, 355 and 617 min, respectively. It appears that the memory effect could last for 172 min, as it does appear around 40 K. The disappearance of the memory behavior at 100 and 200 K could be because the time interval has exceeded the time that the memory can last or that the temperatures are well above TB. The memory effect in nanoparticle systems has been attributed to the existence of significant dipole interactions among particle superspins and/or the broad distribution of relaxation times in the NP assembly [25]. In the present case, the NPs are very loosely packed and the interparticle interaction is insignificant. Size polydispersity of the assembly then plays a major role in the appearance of the memory effect. The anisotropy energy barriers for random flips of domain superspins can generate not only stretched exponential relaxation of the induced magnetization but also give rise to the memory effect.

Bottom Line: The magnitude of the induced inverse magnetization is very sensitive to the field reduction rate as well as to the thermal and field processes before turning the magnetic field off, and can be as high as 54% of the magnetization prior to cutting off the applied magnetic field.Memory effect of the induced inverse magnetization is clearly revealed in the relaxation measurements.The key to these effects is to have the induced eddy current running beneath the amorphous Ni shells through Faraday induction.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, National Central University, Jhongli 32001, Taiwan. s751734@hotmail.com.

ABSTRACT
We report on the design and observation of huge inverse magnetizations pointing in the direction opposite to the applied magnetic field, induced in nano-sized amorphous Ni shells deposited on crystalline Au nanoparticles by turning the applied magnetic field off. The magnitude of the induced inverse magnetization is very sensitive to the field reduction rate as well as to the thermal and field processes before turning the magnetic field off, and can be as high as 54% of the magnetization prior to cutting off the applied magnetic field. Memory effect of the induced inverse magnetization is clearly revealed in the relaxation measurements. The relaxation of the inverse magnetization can be described by an exponential decay profile, with a critical exponent that can be effectively tuned by the wait time right after reaching the designated temperature and before the applied magnetic field is turned off. The key to these effects is to have the induced eddy current running beneath the amorphous Ni shells through Faraday induction.

No MeSH data available.


Related in: MedlinePlus